1. Technical Field
This disclosure relates to sensing systems and more particularly, to a system for sensing a location of a leak in a pipeline system.
2. Description of the Related Art
It is common practice to install liquid and gas pipelines underground or underwater, both to defeat the possibility of tampering, and as may be necessary for regulatory or logistical reasons (e.g., passing under a river). In such cases, when a leak occurs, the actual source of the leak may not be visible. Under such a circumstance, remediation of the leak, once detected by other means, will not be possible until the actual source is located.
Since time is of the essence when remediation is required, to limit the amount of the spill, a system that identifies the location is essential. Since pipelines can run through difficult terrain, such as underwater or in jungle areas, knowing the exact location is a significant factor in permitting fast remediation. High precision avoids the need for time consuming digging of substantial amounts of territory to find the leak.
It is well known that pipelines are under some degree of pressure, either from the pumping of the gas or liquid, or by the effect of gravity. Accordingly, when a pipeline ruptures, it is generally accompanied by the reduction of pressure at the point of the leak. This generates a low-pressure wave that travels in both directions, at the speed of sound in the medium, plus or minus the effect of actual flow rate in the downstream and upstream directions respectively.
In pipeline systems, which may extend over many miles or just a few hundred feet, it is necessary and often imperative to be able to accurately detect the location of a leak. Leaking pipes may cause dangerous conditions, or environmental issues if not properly addressed in an expedient manner.
In the transport of hydrocarbons,.such as oil, leaks may be detected at monitoring stations, which are distributed at intervals along the pipeline. Changes in pressure or flow rate are detected and anomalies are determined to determine leaks in the pipeline. Pressure changes are determined between monitoring stations; however, with conventional detection systems when the leak has first occurred is not known. Accordingly, location of the leak is difficult to determine with the accuracy needed for a quick response. With conventional systems, a leak""s location can be determined in a region on the order of hundreds of meters (e.g., 150 to 200 meters).
Therefore, a need exists for a system and method for accurately determining the location and time of occurrence of a leak in a pipeline system.
A system and method which defines the location in a pipeline, at which a leak has occurred, with very high precision, using the detection of the low-pressure wave resultant from the leak is disclosed. The low-pressure wave travels at the speed of sound in the liquid or gas in the pipeline in both upstream and downstream directions. Site stations that can detect the arrival time of the pressure wave are located at opposite ends of the pipeline segment. The Site Stations detect the arrival time of the low-pressure wave non-intrusively, and with great precision.
Transmission of the sensed data to a master station permits the computation of the location to within the precision permitted by the time resolution that the low-pressure wave is detected. A global positioning system (GPS) mapping system is employed to permit rapid access to the site of the leak by either helicopter, truck or boat, as may be appropriate.
A system and method for determining a time of occurrence of a pressure wave in a pipe provides a first sonic transducer and a second sonic transducer at each of a plurality of site locations along a pipe. Sonic waves are generated through a pipewall at a known desired rate. At each of the plurality of site locations, the sonic waves travel from the first sonic transducer to the second sonic transducer through a liquid flow in the pipe. A measure of travel time is set for the sonic waves. The measure is compared to each of the successive travel times for the sonic waves as the sonic waves arrive at the respective second transducers. A string of counts is output at each second transducer. Each count includes a first count value if a present sonic wave has a travel time that is late as compared to the measure.
A time of occurrence of the pressure wave is determined based on a reference clock when the string of counts includes a string of first count values longer than a threshold value. The time of occurrence of a pressure transient is indicated by a first count in the string of first count values. The time of occurrence is employed in accurately calculating the position of a leak, hot tap or malfunctioning valve, pump, etc.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.